Make compatible with CMake 4.0

[mvieth]

When trying to build with CMake 4.0, the following error is shown:

CMake Error at CMakeLists.txt:2 (cmake_minimum_required):
  Compatibility with CMake < 3.5 has been removed from CMake.

  Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax
  to tell CMake that the project requires at least <min> but has been updated
  to work with policies introduced by <max> or earlier.

  Or, add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to try configuring anyway.

This change raises the minimum required CMake version to 3.5 and thus makes the project compatible with CMake 4.0

[jwhui]

We are running into this issue as well in our projects.

[xavierchanth]

Same here, it seems some GHA runners are using cmake v3.31.6, some are using 4.0.0 (ubuntu-latest).

[joelguittet]

Confirming this issue on my side 👍

[benbuck]

In case it helps anyone else that is using cJSON in their project from CMake, you can work around this issue using a CMake file plus a patch file, something like this:

CMake file:

include(FetchContent)
find_package(Patch REQUIRED)

FetchContent_Declare(
    cJSON
    GIT_REPOSITORY https://github.com/DaveGamble/cJSON.git
    GIT_TAG v1.7.18
    PATCH_COMMAND "${Patch_EXECUTABLE}" -p1 < ${CMAKE_CURRENT_SOURCE_DIR}/cJSON.patch
    UPDATE_DISCONNECTED 1
    EXCLUDE_FROM_ALL
)

FetchContent_MakeAvailable(cJSON)

Patch file:

diff --git i/CMakeLists.txt w/CMakeLists.txt
index 36a6cb5..9428da5 100644
--- i/CMakeLists.txt
+++ w/CMakeLists.txt
@@ -1,2 +1,2 @@
 set(CMAKE_LEGACY_CYGWIN_WIN32 0)
-cmake_minimum_required(VERSION 3.0)
+cmake_minimum_required(VERSION 3.10)

And of course you can customize the CMake file and patch file to suit your project needs.

-Benbuck

[hhoffstaette]

I just saw that this PR only updates to 3.5 - it should probably be 3.10, otherwise cmake-4 will complain about more pending deprecation. It did for me when I reported what became our fix in Gentoo :)

[mvieth]

I just saw that this PR only updates to 3.5 - it should probably be 3.10, otherwise cmake-4 will complain about more pending deprecation. It did for me when I reported what became our fix in Gentoo :)

That is a valid point, and I am happy to change this pull request to make 3.10 the minimum required version if a maintainer of this repo requests it. I originally chose 3.5 because it is the lowest version that makes CMake 4.0 work, and building with CMake 3.5-3.9 is still possible. So in a sense, 3.5 is the more careful, conservative choice, and I thought it had more chance at getting accepted 🙂

[joelguittet]

Agree with @mvieth and 3.5 is also common choice if you look at other libraries.

[michelepagot]

#949